Process for preparing cephalosporin derivatives

ABSTRACT

A process for the preparation of a 7 Beta -acylamidocephalosporin having a 7 Beta -substituent selected from 5carboxy-5-oxopentanamido and 4-carboxybutanamido includes the step of contacting a corresponding compound having a 7 Beta -(D5-amino-5-carboxypentanamido) group with activated cells of Trigonopsis variabilis under aerobic conditions, catalase activity being present in said cells when the desired product has a 7 Beta -(5-carboxy-5-oxopentanamido) group.

United States Patent [1 1 Fildes et al.

[ Apr. 2, 1974 PROCESS FOR PREPARING CEPHALOSPORIN DERIVATIVES [75] Inventors: Robert Anthony Fildes, Bouth near Ulverston; James Rowland Potts,

Marlow; John Eaton Farthing, Southall, all of England [73] Assignee: Glaxo Laboratories Limited,

Greenford .Middlesex, England [22] Filed: Apr. 18, 1972 [21] Appl. No.: 245,258

[30] Foreign Application Priority Data Apr. 2l, 1971 Great Britain 10566/71 Mar. 28, 1971 Great Britain 10566/71 [52] U.S Cl. 195/29, 195/36 R [51] Int. Cl C12d 9/00 [58] Field of Search 195/29, 36 R [56] References Cited UNITED STATES PATENTS 3,658,649 4/1972 Arnold et al 195/29 Primary Examiner-Alvin E. Taneholtz Attorney, Agent, or FirmBacon & Thomas [57] ABSTRACT group.

7 13 Claims, No Drawings PROCESS FOR PREPARING CEPHALOSPORIN DERIVATIVES This invention is concerned with an enzymic oxidation process for the production of derivatives of the antibiotic cephalosporin C.

The cephalosporin compounds referred to in this specification are generally named with reference to cepham (see J.Am.Chem.Soc. 1962, 8 4, 3,400). The term cephem refers to the basic cepham structure with a single double bond. g

Cephalosporin C [3-acetoxymethy l-7B-(D-S-amino- 5-carboxypentanamido) ceph-3-em-4-carboxylic acid]may be prepared by fermentation and then employed as the starting material for the preparation of a wide variety of cephalosporin derivatives. As is well known, the 3-acetoxymethyl group may be converted to unsubstituted methyl or methyl substituted with a variety of substituents'as described in the literature. Moreover, it is often desired to modifythe 7/3-(D 5- amino-5-carboxypentanamido) group of cephalosporin C, either before or after any modification at the 3- cess for the-oxidation of the 7B-side chain of cephalosporin compounds having a 7B-(D-S-amino-5- carboxypentanamido) group. The oxidation destroys the zwitterionic character of the side chain and greatly simplifies subsequent N-deacylation.

In copending'US. Pat. application Ser. No. 846,963 filed Aug. 1, 1969 and now U.S. Pat. No. 3,658,649

' dated Apr. 25, 1972, there is disclosed a method of oxidising the side chain on the 7B-amino group in cephalo sporin C enzymically to provide derivatives which may readily be N-deacylated to 7-ACA. According to the aforementioned Specification, a D-amino acid oxidase of fungal origin was employed, the enzyme being released from the fungal cells before use by one of a variety of methods involving lysis of the cells. The enzyme was then purified, if desired, e.g. by fractionation with ammonium sulphate. Such lysis of the fungal cells was considered necessary since the intact cells were not found to bring about the desired reaction.

It has now been found that the side chain on the 7B- amino group of cephalosporin C is oxidised in the presence of activated cells of the yeast Trigonopsis variabi- Iis. By activated is meant that the yeast cells have been subjected to some physical and/or chemical process which makes the D-amino acid oxidase therein available for catalysis of the oxidation of cephalosporin C but does not result in substantial release of the enzyme, i.e., the cells have been permeabilized.

Accordingly one aspect of this invention provides activated cells of Trigonopsis variabilis.

A variety of methods of activation are described hereinafter.

The invention will be described herein with reference to the oxidation of cephalosporin C and derivatives thereof wherein the acetate group in the side chain at the 3 -position has been replaced by the residue of a nucleophile or a hydroxy group or a hydrogen atom, but

or salts thereof, wherein X is an acetate group, the residue of a nucleophile, a hydroxy group or a hydrogen atom and R is the group -CO.'COOl-l or -COOH which comprises subjecting a compound of fori-nulaz- -OOC S CH(CH2)aCO.NH- HaN 0- I on X 7 I or a salt thereof, wherein Xis as defined above, to the action of activated cells of Trigonopsis variabilis under aerobic conditions, 'catalase activity being present 'in said cells when the group R in the desired product is -CO.COOH.

Examples of salts of the compounds (I) and (II) are sodium and potassium salts.

A suitable strain of Trigonopsis variabilis is that-obtained from the Centraal Bureau voor Schimmelcultur, Baarn, Holland, under culture number CBS 4095.

The use of activated cells'of Trigonopsis variabilis instead of a more or less highly purified preparation of the D-amino'acid oxidase has several practical advantages. First the time-consuming and involved purification procedure is eliminated and replaced by a simple activation process.

Secondly, it has been found that the D-amino acid oxidase enzyme in activated cells of Trigonopsis variabilisis less easily inhibited or inactivated than the isolated enzyme when used in broths resulting from the fermentation of Cephalosporium acremonium Brotzu. This is a point of much practical importance, since for convenience it is often desired to oxidise cephalosporin C without isolating it from the fermentation broth. Sucn I isolation is notoriously difficult, by reason of the amremoval of mycelium and precipitation of protein, contained factors which tended to inhibit fungal D-amino acid oxidases. For this reason, a large excess of enzyme was necessary to ensure satisfactory reaction.

By contrast, when activated cells of Trigonopsis variabilis are employed in place of the crude or purified enrecovered and re-used, whereas purification and reuse of the soluble enzyme is of limited practicability.

Thus it will be seen that the use of activated cells to oxidise cephalosporin C constitutes a substantial advance in the art of cephalosporin chemistry.

The process of activating the cells of Trigonopsis variabilis may be conducted in a number of ways. e.g. as described herein. It is not known what mechanism is involved, but the effect is that the required enzyme is made available for oxidation of cephalosporin C, while non-activated, intact, cells have no activity in this reaction. It must be emphasised that the D-amino acid oxidase does not appear to be liberated into the exocellular fluid by the process of activation: the activity is associated with the cells rather than the supernatant,

which can be replaced without affecting the activity.

- D-amino acid oxidase released therefrom by lysi's, e.g.

by ultrasonication. In the presence of inhibitors found in cephalosporin C fermentation broths, the activity of the activated cells is superior.

The activation process is brought about by subjecting the cells to certain mildly injurious conditions which are not however extreme enough to cause lysis. Examples of such treatments are:

a. Freezing followed by thawing at acid pH e.g. about pH 3 4; the freezing may be at a temperature below l, e.g. about 20 C. The freezing should be of sufficient duration to be effective, e.g. at least one hour at -20.

b. Treatment of the cells in an aqueous phase with one or more organic solvents. Suitable solvents include lower aliphatic ketones e.g. acetone; aliphatic and araliphatic monoand poly-hydric alcohols e.g. 2-phenylethanol or lower alcohols such as n-butanol; and aliphatic or aromatic hydrocarbons e.g. cyclohexane, benzene or toluene. Toluene is the preferred solvent. Treatment at a temperature below 60 C, e.g. at about 37 C for about 30 minutes, will often be found to result in activation without substantial lysis.

c. Treatment with a surface active agent. The agent may be employed as an aqueous solution at a concentration of e.g. '0.0l20 percent, preferably 0.l-l0 percent and advantageously 1 percent (all percentages being by weight or volume. as appropriate). The time and temperature of treatment may be as described under (b). Suitable cationic surfactants include quaternary ammonium compounds e.g. cetyltrimethylammonium, cetylpyridinium and cetyldimethylbenzylammonium halides.

As suitable anionic surfactants may be mentioned higher alkyl sulphates having e.g. 10-18 carbon atoms, for example dodecyl sulphate. Such compounds will generally be used as their salts with inorganic or organic bases, e.g. as alkali metal or ethanolammonium salts. Other anionic surfactants which may be found of value include alkali metal e.g. sodium salts of alkylaryl sulphonates or of sulphonated castor oil and alkali metal salts of bile acids such as sodium desoxycholate.

Non-ionic surfactants e.g. sorbitan monolaurate, Triton X a condensation product of iso-octylphenoxypolyethoxyethanol and ethylene oxide manufactured by Rohm and Haas Company, Philadelphia, USA.) or digitonin may be used.

d. Treatment with alkali. Raising the pH of the medium in which the yeast is suspended has been found to activate the cells satisfactorily. A suitable alkali is an aqueous alkali metal hydroxide e.g. sodium or potassium hydroxide, and an effective concentration is about N/ 100. Quaternary ammonium hydroxides or alkali metal carbonates may also be used. The time and temperature of treatment may be as described under (b).

e. Osmotic shock. Activation may be brought about by subjecting the Trigonopsis cells to extremes of osmotic pressure. The cells may for instance be suspended in a solution of high osmotic pressure e.g. a 2M sucrose solution buffered to pH 8, for a short period of time. e.g. 30 minutes, after which the suspension is rapidly diluted with water.

It maybe necessary to ascertain the optimium conditions of activation for the chosen activation method by trial and error experimentation. It should be appreciated that the activation may be affected by various fac tors including temperature, duration of treatment, pH

of environment and concentration of reagent. Regard- DL)-methionine; possibly this compound acts to induce enzyme formation. The level of D-amino acid oxidase activity depends markedly on the conditions of culturing.

D-Amino acid oxidase activity may be estimated most satisfactorily by determining the rate of formation v by hydrogen peroxide spectrophotometrically using the hydrogen donor o-phenylenediamine as indicator.

In the presence of peroxidase, o-phenylenediamine is oxidised by the hydrogen peroxide to form a brown dye.

Compounds of formula (I) wherein R is the group -CO.COOH are prepared by reacting the appropriate compound of formula (II) with D-amino acid oxidase in the presence of catalase. The latter enzyme is normally present in the activated yeast cells, but extra catalase may be added if required. The amount of additional catalase required may readily be determined by preliminary trial and experiment. The function of the catalase is to prevent oxidative decarboxylation resulting in the formation of compounds of formula (I) in which R is the group -COOH instead of the desired compounds (R is the group -CO.COOH); the compounds of formula (I) in which R is the group -CHO are intermediates in this oxidative decarboxylation.

Compounds of formula (I) wherein R is the group -COOH are prepared by inhibiting any catalase present in the yeast cells. Even when the catalase has been inhibited, the product generally Contains a minor proportion of a-keto acid (R -CO.COOH). Inhibition may be brought about by chemical or physical means.

Suitable catalase inhibitors are ascorbic acid, 3- amino-l,2,3-triazole and inorganic azide. Alkali metal azides, particularly sodium azide, are preferred. The inhibitor may be present in the reaction mixture during the conversion of the cephalosporin starting material to the desired compound or may be used to pretreat the Trigonopsis variabilis cells prior to their use in the conversion.

Thus sodium azide may be added to the reaction mixture at a level of for example, 1 mM to 100 mM, or, if one wishes to avoid the presence of relatively large quantities of azide in the reaction mixture, the sodium, or other alkali metal, azide can be added to a suspension of the activated Trigonopsis cells and allowed to remain in contact with them until no substantial catalase activity can be detected. We have found it convenientto add up to molar concentrations of sodium azide e.g. 500 mM to a cell suspension in buffer solution and leave for 15 hours at a temperature between C and 40 C e.g. 4 C.

Alternatively the catalase in the yeast cells may be deactivated by heat treatment, prior to the use of the cells in the conversion process. We have found that the D-amino acid oxidase and catalase present in the cells have different heat stabilities and this differential enables one to inactivate the catalase preferentially. Thus if the cells are incubated at 40-60, preferably at about 50for at least 3 hours their catalase activity is markedly reduced, while D-amino acid oxidase activity remains. Although the heat treatment may be carried out on cells in a simple aqueous or buffered suspension it is particularly convenient to subject the cells to the treatment while they are simultaneously undergoing treatment with an activation" reagent. For example activation treatment with a solvent such as toluene may be carried out at 50 C for 4 hours to achieve simultaneous inhibition 'of catalase and cell activation.

The reaction of the enzyme system of the activated cells with the compound of formula (II) may be effected at a pH of from 4 to 9 and e.g. 6 to 8. Temperatures between ambient and about 65 C, e.g. 30 40 C, may be used..However, both with regard to pH and temperature, conditions must not be selected which result in deactivation of the enzyme. An enzyme level of not less than 5 units/mg. (as defined below) of isolated cephalosporin starting material should preferably be utilised. At this level, a reaction time of at least 3 hours may be necessary. With higher enzyme levels, e.g. 6

500 preferably about 100 units/mg, shorter reaction COOH group are not very stable and the reaction conditions, and especially the reaction times (which should be short e.g. 'r 2 hours), need to be carefully chosen.

As already mentioned, cephalosporin C is difficult to extract from fermentation broths due to its amphoteric structure and hydrophilic nature. The process of the present invention may be effected in situ (before or after removal of the mycelium) in a cephalosporin C fermentation broth under appropriate conditions and the resulting compounds of formula (I) (X acetoxy) recovered. The process is normally effected after acidification and filtration of the broth. Thereafter the resulting compounds of formula I may be recovered by solvent extraction or by adsorption on a column of ion exchanger.

The compounds of formula (I) where X is an acetate group may be conveniently extracted from the aqueous solution in which they have been prepared, for example by acidification to a pH of 2.5 or less and extraction with an appropriate organic solvent, e.g. ethyl acetate or n-butanol. Multiple extractions with ethyl acetate will give substantially complete extraction, but the efficiency can be improved by making the aqueous phase saturated, or substantially saturated, with a water soluble inert inorganic salt e.g. sodium chloride.

In isolating the products from both fermentation broths and simple aqueous solutions, a system using a combination of an ion-exchanger and solvent extraction has been found to give good results. Suitable ionexchangers are the high molecular weight liquid amine anion exchangers sold by Rohm and Haas Co. under the names Amberlite LAl, LA2, and LA3 (LAl and LA2 are secondary amines; LA3 is a primary amine). Preferred solvents for use in conjunction with the liquid anion-exchangers are n-butanol and butyl acetate.

A system which has been used with particular advantage in extractions from deproteinised cephalosporin fermentation broths is Amberlite LAl in n-butanol, followed by back extraction with sodium bicarbonate solution and subsequent extraction into ethyl acetate. The pH of the broth is preferably reduced below 6 and most advantageously to 3-5 before extraction.

The solid resin, Amberlite XAD2, which is a macroreticular, cross-linked polystyrene polymer, may also be used in extracting compounds of formula (I) where X is an acetate group from crude or deproteinised cephalosporin fermentation broths. A suitable solvent for eluting the adsorbed compound from the resin may be determined by preliminary experiment. In the case of 3-acetoxymethyl-7B-(4-carboxybutanamido)ceph- 3-em-4-carboxylic acid a suitable solvent is acetone.

The compounds of formula (I) where X is the residue of a 'nucleophile or a hydroxy group or a hydrogen atom may be recovered from the aqueous media in which they have been prepared in a similar manner to that described above. This will depend on the nature of the X group and variations in the extraction conditions may be necessary. These can readily be determined by preliminary trial and error experiments.

Compounds of formula (I) in which R is -COOH may be converted into the corresponding 7B-amino compounds by reacting the corresponding 4-ester with an imide-halide forming component, converting the imide halide so obtained into the imino ether and decomposing the latter. if desired, the ester group may be split off by hydrolysis or hydrogenolysis (if suitable) to yield the 4-carboxylic acid.

Suitable imide halide forming components include acid halides derived from the phosphorus acids, the preferred compounds being the chlorides such as, for

example, phosphorus oxychloride or phosphorus pentachloride.

This method of N-deacylation is described in greater detail in British Pat. Nos. 1,041,985 and 1,1 19,806; Belgian Pat. No. 719,712 and in South African Pat. specifications Nos. 68/5048 and 68/5327.

Compounds of formula (I) in which R is -CO.COOH are preferably reduced, for example using an alkali metal borohydride, to the corresponding compounds in which R is -CH(Ol'-l)COOl-l, before the modified side chain is removed by the method described in Belgian Pat. No. 719,712.

In consequence, important compounds of formula (1) are those in which (A) R is -CO.COOH and X is an acetate group, namely 3-acetoxymethyl-7B-(5-carboxy-5- oxopentanamido) ceph-3-em-4-carboxylic acid and (B) R is -COOl-l and X is an acetate group, namely 3- acetoxymethyl-7B-(4-carboxybutanamido) ceph-3-em- 4-carboxylic acid. These compounds are key intermediates in the production of 7-ACA from the naturally occurring cephalosporin C. Compound (B) (R -COOH) is especially important in this respect.

The starting compounds of the process according to invention wherein X is the residue of a nucleophile may be prepared by reacting cephalosporin C with a nucleophile. Examples of such nucleophiles are: l) Pyridine or other hetrocyclic weak tertiary bases as described in British Pat. No. 912,541, i.e., a heterocyclic compound having a weakly basic tertiary nitrogen atom as a member of a heterocyclic ring system and being a weaker base than ammonia. The heterocyclic weak tertiary base may contain e.g."an acidic, sulphonamido or basic substituent (in addition to the tertiary nitrogen atom).

Such heterocyclic weak tertiary bases include pyridine, nicotinamide, nicotinic acid, collidine, quinoline, pyrimidines, thiazoles and sulphonamide derivatives of the foregoing bases, such as sulphadiazine, sulphathiazole and sulpha-pyridine. 2) Sulphur-linking, nitrogen linking or inorganic nucleophiles as described in British Pat. No. 1,012,943, viz. (a) thiourea and substituted thioureas including aliphatic, aromatic, alicyclic and heterocyclic substituted thioureas'; (b) aromatic and aliphatic thioamides e.g. thioacetamide and thiosemicarbazide; (c) thiophenol and substituted thiophenols; (d) substituted and unsubstituted primary and secondary aromatic amines, preferably free from tertiary nitrogen heterocyclic substituents; (e) thiols and substituted thiols, particularly amino thiols and substituted aminothiols; (f) metal salts, particularly alkali metal salts, of azide ion (N hydrogen phosphate ion (HPOf), and thiosulphate ion (8 (g) pyrroles and substituted pyrroles, e.g. alkyl pyrroles.

Suitable nucleophiles of group (a), the thioureas, include members of the formula dipheny-lthiourea and ethylene thiourea.

The substituted and unsubstituted primary and secondary amines (d) may be exemplified by aniline, pnitro aniline p-nitro-N-methyl aniline, sulphanilic acid and p-amino benzoic acid; the group also covers the naphthylamines such as a-naphthylamine and substituted naphthylamines.

Substituted thiols include aminothiols and substituted aminothiols as nucleophiles of group (c). Examples of such nucleophiles include 2-aminoethanethiol, 2-amino-2-methyl-propanel-thiol, 3- dimethylaminopropane-l-thiol and 2-piperidinoethane- 1 -thiol.

The anions employed as nucleophile in the form of their metal salts are preferably in the form of their alkali metal salts, e.g. sodium salts.

As substituted thiophenols may be mentioned those substituted in the nucleus with an amino or substitued amino group e.g. alkylamino or dialkylamino. Simple examples of such thiophenols are therefore 0- and pamino thiophenol, also compounds derived from thiophenols containing conjugated electron attracting group, i.e., such a group in an 0 or p-position or, if desired, in more than one such position. Important examples of this type of nucleophile are various nitrothiophenols e.g. o-nitrothio-phenol and o,p-dinitrothiophenol.

The term electron attracting group is, of course, well-known in organic chemistry and refers to a substituent which attracts electrons more than hydrogen does (see for example A. M. Remick Electronic Interpretations of Organic Chemistry," John Wiley & Sons lnc., New York, 1943).

Examples of electron attracting groups which may be present on the above nucleophiles are nitro groups, nitroso groups, carbonyl groups, carboxyl groups, cyano groups and trifluoromethyl groups. Important members of the sub-class (e) are compounds derived from heterocyclic compounds containing appropriate substituents and which are 5- or 6-membered rings and heterocyclic compounds of this type fused to a 6-membered carbocyclic ring e.g. a benzene ring. Hetero atoms which may be present in the ring include nitrogen, sulphur and oxygen at least one of which must be nitrogen. Usually the mercapto group will be attached to a carbon atom of the heterocycle and a heterocyclic nitrogen atom will be adjacent to this carbon atom. The heterocycle may contain other substituents e.g. N- alkyl, ketonic oxygen, etc. The sub-class therefore includes derivatives of thiazoline, hydantoin, imidazole, thiazole, oxazole, etc. but it should be understood that it does not include cyclic thioureas.

Examples of heterocyclic nucleophiles which may be used thus include 2- mercaptothiazoline, 2- mercaptohydantoin, 1-methyl-2-mercapto-imidazole, 2-mercapto-imidazole, 2-mercapto-benzimidazole, Z-mercapto-benzothiazole, Z-mercaptobenzoxazole and Z-mercapto-pyridine.

Examples of such nucleophiles thus include:

Nada 0' heterocyclic compounds are described as mercapto or thione compounds for reasons of convention. 3) Sulphur-linking nucleophiles as described in British Pat. No- 1,059,562 of the formula (in which M is an alkali metal or an ammonium group, R is a hydrogen atom or an aliphatic, araliphatic or aryl group and R is an aliphatic, araliphatic or aryl group or R and R together form a divalent group).

The group M in the above formula is conveniently sodium or potassium.

Where R and/or R is an aliphatic group this is preferably an alkyl group containing l-6 carbon atoms e.g. methyl. Where either group is an araliphatic group this may be a benzyl group and where either group is an aryl group this may be a phenyl group. As is stated above R and R may together form a divalent group. This may be a divalent hydrocarbon group e.g. {Cl-1 where n is 4 or 5 or a C-alkylated, aralkylated orarylated derivative thereof. Thus R and R together with the adjacent nitrogen atom may form a piperidino group.

Compounds of the above formula are conveniently prepared according to the following equation:

(where R, R and M have the meanings defined above). They are advantageously used in the form of their alkali metal salts. 4) Nitrogen linking nucleophiles as described in British Pat. Nos. 1,030,630, 1,082,943 and 1,082,962. These are nucleophiles (a) of several formula 1 where Z is a loweralkyl, carbamoyl, N-monoloweralkylcarbamoyl, N,N-dimethylcarbamoyl, loweralkoxycarbonyl, hydroxyloweralkyl, N-(hydroxyloweralkyl) carbamoyl or'carbamoylloweralkyl group and p is 0, l, 2 or 3,

It should be understood that the pyridine group may be substituted with two or more different species of the group 2.

The terms lower alkyl and lower alkoxy" as used above indicate groups containing 1-6 carbon atoms, preferably 1 or 2 carbon atoms.

(b) of formula:

wherein R is an alkyl, hydroxyalkyl, N-hydroxyalkylcarbamoyl or alkanoyloxy group, said alkyl moieties containing not more than four carbon atoms and, x is 1 or 2. Where x 2 the R groups need not be the same.

(0) of general formula where R is a carbamoyl group, a carboxy group or a lower alkoxycarbonyl group and x is 1 or 2.

Where x 2 the R groups need not be the same. 5) Sulphur linking nucleophiles as described in British Pat. No. 1,101,423 of formula R YH where Y is the group -SO -;-S-SO or -S-CX-, X being a sulphur or oxygen atom; R is an aliphatic, aryl, araliphatic, heterocyclic, or heterocyclic substituted aliphatic group or, where Y is the group -SO -S-CS-, a hydroxy group or alkoxyl group respectively.

The heterocyclic moities are preferably 5- or 6- membered rings.

The group R is preferably an aryl e.g. phenyl or heterocyclic group, especially in the case of compounds where Y is the group -S-CX.

tuted with cyano, nitro, lower alkoxy or lower alkylthio. The term lower indicates that the groups in question have1-4 carbon atoms. The group Y-R may have the formula where m is O or 1, Q is oxygen, sulphur, NI-l or N-alkyl (C -C and R and n have the above meanings. Where Q=NH it may be necessary to protect the hydrogen atom during the preparation of the thio-acid.

This list of nucleophiles is not limiting and is given purely by way of illustration. Where X is a hydroxy group the compound may be prepared by the methods described in British Pat. No. 1,121,308, that is by hydrolysing cephalosporin C with an esterase derived PRELIMINARY Cultures were grown initially in shake flasks, and subsequently in stirred fermentors, containing the medium described by Sentheshanmuganathan and Nickerson (1962), J. Gen. Microbiol. 27, 465, with either methionine or alanine as the nitrogen source.

ESTIMATION OF D-AMINO ACID OXIDASE ACTIVITY Amino acid oxidase (AAO) activity was determined spectro-photometrically by following the rate of formation of hydrogen peroxide (H I The method is based on the coupled reactions shown in equations 1 and 2.

A0] 4 Amluoacld H20 0 a-Kcto acid NH; H101 (2) [POD] IMO; DII; 21120 1) Hydrogen peroxide in the presence of peroxidase (POD) oxidises the hydrogen donor 0- phenylenediamine (DH to a brown dye (D).

The assay was carried out at 37 in a glass cuvette with a 1 cm light path and the formation of the brown dye was followed at 420-nm. The reaction mixture consisted of 1.0 ml 0.1 M sodium pyrophosphate buffer pH 8.1, 0.5 ml o-phenylenediamine solution (0.02 percent o-phenylenediamine in water), 0.3 ml substrate (1 percent potassium cephalosporin C or 2 percent D-alanine in sodium pyrophosphate buffer pH 8.1), 0.01 ml peroxidase (10 mg/ml aqueous solution) and sufficient water to make the final volume 2.8 ml.

The reaction was started by the addition of 0.2 ml enzyme solution to the reaction mixture. The blank was run under identical conditions using water in place of the substrate.

The linear increase in optical density at 420 nm during the first 5 minutes was used to measure the AAO activity.

A unit of enzyme activity is defined as the quantity of enzyme which, at 37 and pH 8.], produces a change in optical density of 0.00l/min.

ACTIVATION OF TRIGONOPSIS VARIABILIS Samples ml) of whole Trigonopsis variabilis fermentation broth were centrifuged (1,400 g) for 5 minutes and the supernatants discarded. The wet pellets of sedimented cells so formed were subjected to various treatments, as follows:

a. stored at 4 C and then suspended in water (10ml) b. suspended in 0.01 M sodium pyrophosphate buffer, pH 8.1 (10 ml) and sonicated for 30 minutes at 20 KHZ in an M.S.E. (Model 60W) ultrasonic Disintegrator, then clarified by centrifugation c. frozen at 20C for not less than 1 hour then thawed by standing at room temperature and suspended in water (10 ml) d. suspended in the following reagents (10 ml) at 4 C for 24 hours, centrifuged for 5 minutes at 1,400 g. and the cells resuspended in water (10 ml):

Digitonin (1 percent, w/v) Span 20 (1 percent, v/v) (a surfactant, viz sorbitan monolaurate) NaOH (N/ 100) Cyclohexane percent, v/v; i.e., 9.5 ml cyclohexane and 0.5 ml water) Acetone Benzene (2 percent, v/v) and n-butanol (4 percent,

n-Butanol(2.5 percent, v/v) and toluene (1 percent,

All the samples were assayed for D-amino acid oxidase activity. The results are shown in the following Table I.

Further work on activation of Trigonopsis variabilis wasperformed using cultures of higher D-amino acid oxidase activity. The activating agents were (a) surface active agents; (b) organic solvents; and (c) osmotic shock SURFACE ACTIVE AGENTS 10 ml. samples of a culture broth of Trigonopsis variabilis (stored at 4 C) were centrifuged (1,400 g.) forS minutes and the supernatant discarded. The cell pellet was resuspended in an 0.1 percent solution of the appropriate surface active agent in 0.1M sodium pyrophosphate buffer, pH 8.1, and incubated at constant temperature for a fixed length of time. The cell suspension was agitated for 30 seconds at the beginning of the incubation period and then at 5 minute intervals throughout the incubation. In all cases the conditions of incubation were as follows:

'5 min 4 C 30 min 4 C 5 min 37 C 30 min 37 C Following incubation, the cell suspension was cooled (where appropriate) to 4 C, centrifuged (1,400 g.) for 5 minutes and the supernatant carefully decanted off and discarded. The cell pellet was then washed by resuspending in distilled water, centrifuged for a further 5 minutes, and the supernatant decanted off. The final cell pellet was resuspended in 0.01M sodium pyrophosphate buffer, pH 8.1, and diluted to give 50 units/ml of activity. All determinations of D-amino acid oxidase activity were performed using the spectropho- Further activation tests were carried out using a solutometric assay described previously. tion of Triton X100. All treatments wereper formed in duplicate and the Samples ml.) of T. variabilis fermentation broth final result expressed as a mean value. were centrifuged at 1,400 g for 5 minutes and the su- The final suspension was examined microscopically 5 pernatant discarded. The wet cell pellets so formed and in all cases the cells appeared to have remained inwere suspended in 0.1M sodium pyrophosphate buffer tact and were indistinguishable at a magnification of .1: pH 8.1 ml) containing Triton X100. The activation 900 from untreated cells, but some change in internal conditions and treatment of the cells before assay were structure was detected by an electron microscope. 10 carried out as described immediately above except that The D-amino acid oxidase activities arising from difthe incubations were carried out only at 4 and 37 for ferent methods of treatment were compared with the i30 minutes. The results were as follows:

ti 't f t at 11 a d ith th t 't of a ac V] y 0 un re ed ce s n w e ac 1V1 y TABLE 1(a) crude cell-free enzyme preparation. In the latter case the enzyme was released from the cells by ultrasonic disintegration for 30 minutes at 4 C in the presence of amino acid oxidase activity 0.01Msodium pyrophosphate buffer, pH 8.1. This son- Triton x100 (units/ml) icated extract was clarified by centrifugation at 38,000

concentration g. for 15 minutes at 4 C prior to assay. The results werev 2O (9%,) Activation at Activation in as follows:

TABLE I] (a) 1.0 1,680 15,600

, 10.0 4,200 20,800 D-amino acid oxidase activity, i Surface Units/m1 and treatment time/temp 4,600 22,000

active agent: 2.2.2.2..

5 min] min/ 5 min/ 30 min/ 1 TABLE III (13) Cetyltrimethyl 2,070 3,120 2,380 2,590 ammfimium I I Controls D-amino acid oxidase activity bromide I (units/m1) Cetyl 2,380 2,250 2,520 2,260 pyridinium Untreated cells No detectable activity chloride Cetyldimethyl 2,320 2,350 2,130 2,520 c fr enzyme 7 22 300 benzylammonium preparation chloride i Sodium 1,200 1,080- 1,010 1,260

desoxycholate Digitonin 1,100 1,410 1,970 2,260 40 Sodium dodecyl sulphate .9 1.870 2.090 2.160 Samples from a culture broth were prepared as described-in section (a) above except that incubation was yfi m I performed in the presence of various organic solvents TABLE I] (b) 5 at two different concentrations. Prior to incubation the rophosphate buffer, pl-1"8.1, and to this suspension the d I I v Comm MeanDammo w appropriate solvent (1 percent or 10 percent) was oxidaae activity, Units/ml added (irrespective of whether or not the mixturewas miscible.) I

'f'" washed. cell pellet was resuspended in 0.1M sodium py- The results were as follows; n.d. indicatesno deactivity ecu-rice enzyme tectable activity.

preparation 1,920-

Solvent D-amino acid oxidase activity, Units/m1 and treatment time/temp Concn 5 min/ 30 min/ 5 min/ 30 min/ TABLE 1V(b) Mean D-amino acid Controls oxidase activity,

(Units/ml) Untreated n.d.

cells cell-free enzyme 3,730

preparation TABLE V(a) OSMOTIC SHOCK The following buffer solutions were employed; trisl-lCl indicates 1, 1 -di( hydroxymethyl )-2- hydroxyethylamine hydrochloride and EDTA indicates ethylenediaminetetraacetic acid. Buffers (2) and (4) were of high osmotic pressure by reason of containing 2M sucrose.

TABLE Vl(a) Buffer 0.01 M Tris- 0.01M

HCL pH 8.0 sucrose MgSO, EDTA Samples (5ml) of T. variabilis fermentation broth were centrifuged at 1,400 g for 5 minutes and the supernatants discarded. The wet pellets so formed were resuspended in buffers (l) or (3) ml) and again centrifuged. This washing procedure was repeated, the cell pellet finally resuspended in buffers l (2), (3) or (4) (10 ml) and incubated for 30 minutes at 37 C.

Each suspension was then diluted to 100 ml with cold buffer (1) or (3) and 10 ml samples removed. After centrifugation at 1,400 g the cell pellet was resuspended in 0.01M sodium pyrophosphate buffer, pH 8.1 and diluted with buffer before assay.

The following results were obtained. For comparison a 5 ml sample of fermentation broth was converted to a cell free enzyme preparation.

TABLE VI( b) Buffer used in incubation D-amino acid oxidase activity (units/ml l n.d. (2) 5,600 n.d. 6,050 Cell free enzyme preparation 23,600 Untreated cells n.d.

OXIDATION OF CEPHALOSPORIN C EXAMPLE 1 a. Trigonopsis variabilis (CBS. 4095) was grown in a synthetic medium containing methionine, as described in the preliminary to the examples. The cell suspension was harvested by centrifugation, and the wet cell mass retained.

The wet cells were divided into four aliquots and activated by freezing to -20 C followed by thawing at room temperature. After dilution with water this yielded a suspension of cells of6l .7 percent wet wt/vol. When this suspension was assayed using the spectrophotometric assay described previously, it was found to contain 32,200 units enzyme activity/ml.

40 g. of a potassium cephalosporin C preparation, having a purity of 68 percent (i.e., 27.2 g. potassium cephalosporin C) was dissolved in 2 litres of 0.2M sodium pyrophosphate buffer, pH 8.1, containing sodium azide (2 60 r ng.) and diluted to 3,990 ml with water. The solution, contained in a stirred vessel was equilibrated in a water bath at 33 C for 30 min. The conversion was started by adding 10 ml of the cell suspension previously described and was continued for 3 hours using an air flow rate of 3 litres/minute together with an agitation rate of 550 rpm. The conversion was terminated by centrifugation of the contents of the vessel at 2,100 g for 1 hour.

Analysis by quantitative (ultraviolet absorption) thin-layer chromatography of samples withdrawn at intervals from the reaction vessel showed that the conversion was complete in approximately 1.5 hours and that 68 percent of the cephalosporin C had been converted to 3-acetoxymethyl-7B-(4- carboxybutanamido )ceph-3-em-4-carboxylic acid. The level of enzyme used corresponded to 12.8 units/mg cephalosporin C (free acid).

The above product was extracted from the clarified conversion mixture as follows:

2 litres of the conversion mixture was adjusted to pH 1.5 using hydrochloric acid and extracted into 8 X 1.6 litres ethyl acetate. The combined ethyl acetate extracts were evaporated under vacuum to approximately 800 ml and dried overnight using anhydrous sodium sulphate. The dried ethyl acetate extract was further evaporated under vacuum to 50 ml and then added slowly to 700 ml light petroleum (60-80) whilst stirring vigorously.

The resulting precipitate was filtered off, and dried under vacuum over alumina to yield 3-acetoxymethyl- 7,8-(4-carboxybutanamido)ceph-3-em-4-carboxylic acid (9.83 g) as a pale yellow solid having a purity of 72 percent.

EXAMPLE 2 Cells of T. variabilis from a 1 litre sample of fermentation broth were harvested by centrifugation at 2,100

g for 30 minutes at 4 C. The supernatant was discarded and the cell pellet resuspended in 1 litre sodium pyrophosphate buffer, pH 8.1. 100 ml aliquots of this cell suspension were added to 10 ml toluene-in 250 ml flasks. The immiscible mixture of toluene and the aqueous cell suspension was incubated on a rotary shaker I -(300'rpm) at 37 C for 2 hours. The contents of the flasks were then cooled to 4 C, centrifuged at 2,100 g for 30 minutes and the supernatant layers removed and discarded. The cell pellet was then resuspended in 100 ml distilled water, re-centrifuged and the supernatant removed and discarded. The cell pellets from all the flasks thus treated were then combined andmade up to a totalvolume-of 200 ml of 0.1M sodium pyrophosphate buffer, pH 8.1. This suspension was assayed and was found to contain 22,880 units enzyme activity/ml.

EXAMPLE 3 4.8 litres culture broth from a fermentation of Cephalosparium acremonium (B'rotzu) was centrifuged at 2,100 g for 1 hour at 4 C and the supernatant retained. The pH of the supernatant was adjusted to pH 4.5 with sulphuric acid and clarified by centrifugation at 2,100 g for 1 hour at 4 C. The supernatant was retained, adjusted to pH 2.8 with sulphuric acid and clarified by centrifugation as described above. The resulting supernatant was adjusted to pH 8.1 with NaOH and again clarified by centrifugation. This protein filtrate (3.23 litres) was shown by microbiological assay to contain 22.3 g potassium cephalosporin C. The protein filtrate was diluted to 3.975 litres by the addition of 0.2M sodium pyrophosphate buffer, pH 8.1, containing a total of 260 mg sodium azide.

The above mixture was oxidised under identical conditions to those described in Examples 1 and 2, the reaction being started by the addition of 23 ml of the cell suspension of toluene-treated cells described in Example 2.

Analysis by quantitative thin layer chromatography of samples withdrawn at intervals from the reaction vessel showed that the conversion was complete in approximately 2.5 hours and that 73 percent of the cephalosporin C had been converted to 3-acetoxymethyl- 18 7B-(4-carboxybutanamido)ceph-3-em-4-carboxylic acid.

The level of enzyme used corresponded to 25.6 units/mg cephalosporin C (free acid).

EXAMPLE 4 A fermentation broth containing cephalosporin C was purified by filtering off the'mycelium and protein (after precipitation). The filtrate, containing 4.8 mg/ml cephalosporin C, was adjusted to pH 8.0 with N NaOH and clarified by centrifugation (18,000 g.).

5 ml of clarified filtrate was mixed with 3 ml of 0.2M- sodium pyrophosphate buffer, pH 8.0,1 ml of 10 mM- sodium azide and 1 ml of frozen and thawed cell suspension (224 units of D-amino oxidase activity), and

was aerated and incubated at 33 C for 4 hours. Examination of the resultant mixture by thin layer chromatography on silica coated plates developed with pe'rcent aqueous acetone showed that percent of the cephalosporin C had been used up and that most of this had been converted to 3-acetoxymethyl-7 B-(5' carboxy-S-oxopentanamido)ceph-3-em-4-carboxylic acid and carboxybutanamido)ceph-3-em-4-carboxylic acid.

EXAMPLE 5 40g of a potassium cephalosporin C preparation, having a purity of 68 percent (i.e., 27.2g potassium cephalosporin C) was dissolved in 1.5 litres of 0.2M sodium phosphatebuffer, pH 8.1. 1 ml catalase solution was added, containing 20,000 units enzyme activity. (1 unit catalase enzyme activity is defined as that which will decompose 1 mole hydrogen peroxide/min. at pH 7.0 at 25).

The solution, contained in a stirred vessel, was diluted to 3,980 ml with water and equilibrated in a water bath at 33 C for 30 min. The conversion was started by adding 20 ml of a cell suspension similar to that described in Example 1. When this suspension was assayed using the spectrophotometric assay described previously it was found to contain 12,100 units enzyme activity/ml. The conversion was continued for 2.5 hours using an air flow rate of 3 litres/minute together with an agitation rate of 550 rpm. The conversion was terminated by centrifugation of the contents of the vessel at 2,100g for 1 hour.

The product was extracted as follows: 3,900 ml of the conversion mixture was adjusted to pH 1.5 using hydrochloric acid and divided into two equal aliquots. Each aliquot was extracted using 7 X 800 ml ethyl acetate and the combined ethyl acetate extracts from 'both aliquots were evaporated under vacuum to approximately 2 litres and dried overnight using anhydrous sodium sulphate. The dried ethyl acetate extract was further evaporated under vacuum to ml and then added slowly to 600 ml light petroleum (60 80)whilst stirring vigorously.

The resulting precipitate was filtered off in two batches and dried under vacuum over alumina to yield 3-acetoxymethyl-7B-(S-carboxy-S-oxopentanarnido) ceph-3-em-4-carboxylic acid as a pale yellow solid. The

two samples of solid obtained (6.89g and 4.96g) had 3-acetoxymethyl-7B-(4- EXAMPLE 6 Production of 3-acetoxymethyl-7B-(4- carboxybutanamido)-ceph-3-em-4-carboxylic acid 1. Using sodium azide as catalase inhibitor Cells of T. variabilis from 2.7 litres of fermentation broth were harvested by centrifugation at 2,100 g for 30 minutes at 4 C. The supernatant was discarded and the cells resuspended in 2.7 litres 0.1M sodium pyrophosphate buffer, pH 8.1. This suspension was incubated in a stirred vessel at 37 and 300 ml toluene was added. The incubation was continued for 4 hours, after which time the vessel contents were centrifuged at 2,100 g for 30 minutes at 4 C, and the supernatant layers removed and discarded. The cell pellets were resuspended in a total volume of 3 litres distilled water, the centrifugation repeated, and the supernatant removed and discarded. The cells were finally resuspended in 500 ml 0.1M sodium pyrophosphate buffer, pH 8.1. When this cell suspension was assayed it was found to contain 24,000 units enzyme activity/ml.

g of potassium cephalosporin C preparation having a purity of 70 percent was dissolved in 2 litres 0.1M

sodium pyrophosphate buffer, pH 8.l, containing 50- dium azide (1.3 g). The solution, contained in a stirred vessel, was equilibrated in a water bath at 33 for 30 minutes. The conversion was started by adding 28 ml of the cell suspension previously described and continued for 2 hours using an air flow rate of 6 litres/minute together with an agitation rate of 550 rev/min. The conversion was terminated by centrifugation of the contents of the vessel at 2,100 g carried out overnight. The level of enzyme used corresponded to 53 units/mg cephalosporin C acid.

Sodium chloride (150 g) was dissolved in 500 ml of the resulting solution, the pH was adjusted to 1.5 using concentrated sulphuric acid and the solution extracted four times with 200 ml portions of ethyl acetate. The bulked extracts were dried overnight at 4 C using magnesium sulphate. The magnesium sulphate was re moved by filtration and the dried ethyl acetate extract evaporated under vacuum to approximately 20 ml. On standing at room temperature the crystalline precipitate which formed was removed by filtration and dried under vacuum to yield the title compound (2.10 g) as a white solid having a purity of 92 percent (E 220 (260 mm)). This corresponded to an overall conversion of potassium cephalosporin C to the above product of 65 percent. v

ii. Using pretreatment with sodium azide to inhibit catalase.

Cells of T. variabilis were activated as described in Example 6(i). Before use in the conversion, sodium azide (6.5 g) was added to the cell suspension (200 ml) and this was stored overnight at 4. C. The cell suspension was then centrifuged at 2,100 g for 30 minutes at 4 C and the supernatant discarded. The cells were resuspended in 200 ml 0.1M sodium pyrophosphate buffer, pH 8.1 and the centrifugation repeated. The supernatant was again discarded and the cells resuspended in 200 ml buffer. This suspension was assayed and found to contain 17,600 units enzyme activity/ml.

20 g of a potassium cephalosporin C preparation having a purity of 70 percent was dissolved in 2 litres 0.1M sodium pyrophosphate buffer, pH 8.1. The conversion was carried out as described in Example 6(i) using 38 ml of the cell suspension. The level of enzyme used corresponded to 52 units/mg cephalosporin C acid.

The resulting solution was extracted as described previously to yield the title compound (2.05 g) as a white solid having a purity of 91 percent (E 217 (260 mm)). This corresponded to an overall conversion of potassium cephalosporin C to the above product of 63 percent.

iii. Using heat treatment to inhibit catalase Cells of T. variabilis were activated as described in Example 6(i) using a temperature of 50 C instead of 37 C. The resulting cell suspension was assayed and found to contain 17,600 units enzyme activity/ml.

20 g of a potassium cephalosporin C preparation having a purity of 70 percent was dissolved in 2 litres 0.1M

sodium pyrophosphate buffer, pH 8.1. The conversion was carried out as described in Example 6(i) using 38 ml of the cell suspension. The level of enzyme used corresponded to 52 units/mg cephalosporin C acid.

The resulting solution was extracted as described previously to yield the title compound (1.85 g) as a white solid having a purity of 92 percent (E 220 (260 mm)). This corresponded to an overall conversion of potassium cephalosporin C to the above product of 57 percent.

We claim:

1. A process for the preparation of a 7B-acylamidocephalosporin having a 7B-substituent selected from the group consisting of 5-carboxy-S-oxopentanamido and 4-carboxybutanamido which includes the step of contacting a corresponding compound having a 7B-(D- 5-amino-5-carboxypentanamido) group with activated intact cells of Trigonopsis variabilis under aerobic conditions, catalase activity being present in said cells when the desired product has a 7B-(5-carboxy-5- oxopentanamido) group. i

2. A process as claimed in claim 1 wherein said cells have been activated by treatment in an aqueous phase with at least one organic solvent selected from the group consisting of ketones, aliphatic and araliphatic monoand polyhydric alcohols, aliphatic hydrocarbons and aromatic hydrocarbons.

3. A process as claimed in claim 2 wherein said organic solvent is toluene.

4. A process as claimed in claim 1 wherein said cells have been activated by treatment with an aqueous solution of a surface active agent at a concentration of 0.1-10 percent.

5. A process as claimed in claim 1 wherein said cells have been activated by freezing at a temperature below l0 followed by thawing at pH 3-4.-

6. A process as claimed in claim 1 wherein said corresponding compound is subjected to the action of said activated cells at a pH of 6 to 8 and a temperature of 30-40.

7. A process as claimed in claim 1 wherein catalase in said activated cells is inhibited or inactivated, whereby a product having a 713-(4- carboxybutanamido) substituent is obtained.

8. A process as claimed in claim 7 wherein said catalase is inhibited by adding sodium azide to the reaction mixture at a concentration of lmM to mM.

9. A process as claimed in claim 7 wherein said activated cells before contact with said corresponding compound have been treated with an aqueous solution of sodium azide of up to molar concentration at a temperature of 0-40.

cells have been activated by osmotic shock.

hibit or inactivate catalase. 12. A process as claimed in claim 1 wherein said cells have been activated by treatment with alkali.

13. A process as claimed in claim 1 wherein said 

2. A process as claimed in claim 1 wherein said cells have been activated by treatment in an aqueous phase with at least one organic solvent selected from the group consisting of ketones, aliphatic and araliphatic mono- and polyhydric alcohols, aliphatic hydrocarbons and aromatic hydrocarbons.
 3. A process as claimed in claim 2 wherein said organic solvent is toluene.
 4. A process as claimed in claim 1 wherein said cells have been activated by treatment with an aqueous solution of a surface active agent at a concentration of 0.1-10 percent.
 5. A process as claimed in claim 1 wherein said cells have been activated by freezing at a temperature below -10* followed by thawing at pH 3-4.
 6. A process as claimed in claim 1 wherein said corresponding compound is subjected to the action of said activated cells at a pH of 6 to 8 and a temperature of 30*-40*.
 7. A process as claimed in claim 1 wherein catalase in said activated cells is inhibited or inactivated, whereby a product having a 7 Beta -(4-carboxybutanamido) substituent is obtained.
 8. A process as claimed in claim 7 wherein said catalase is inhibited by adding sodium azide to the reaction mixture at a concentration of 1mM to 100mM.
 9. A process as claimed in claim 7 wherein said activated cells before contact with said corresponding compound have been treated with an aqueous solution of sodium azide of up to molar concentration at a temperature of 0*-40*.
 10. A process as claimed in claim 7 wherein said activated cells, before contact with said corresponding compound, have been heat treated to inactivate catalase without substantial inactivation of D-amino acid oxidase.
 11. A process as claimed in claim 7 wherein said cells have been simultaneously activated and treated to inhibit or inaCtivate catalase.
 12. A process as claimed in claim 1 wherein said cells have been activated by treatment with alkali.
 13. A process as claimed in claim 1 wherein said cells have been activated by osmotic shock. 